Many integrated circuit processes now provide for both digital and analog functions to be integrated on one circuit. Typically, a merged bipolar-CMOS (hereinafter "BiCMOS") process is used to provide both analog and digital devices. While digital designs seldom need capacitors, analog designs frequently use capacitors.
Heretofore, BiCMOS processes have made only one type of capacitor available, normally a low voltage, high value capacitor. However, it is often necessary to support the analog functions with high voltage capacitors, capable of handling voltages in the twenty-to-thirty volt range.
Importantly, the processes used to form the high voltage capacitors should not affect the characteristics of the bipolar and MOS devices as well as the low voltage capacitors. Otherwise, the use of "standard cells" would be precluded in the design of the circuit. Standard cells are subcircuits which may be used in a variety of applications, thereby reducing design time and increasing reliability.
Therefore, a need has arisen in the industry for a high voltage capacitor for use in BiCMOS and other processes, which may be fabricated on an integrated circuit without altering the characteristics of other devices thereon.